The present invention relates to semiconductor device fabrication and integrated circuits and, more specifically, to methods of self-aligned multiple patterning and structures formed by self-aligned multiple patterning.
A back-end-of-line (BEOL) interconnect structure may be used to connect device structures fabricated on a substrate during front-end-of-line (FEOL) processing with each other and with the environment external to the chip. Self-aligned patterning processes used to form a BEOL interconnect structure involve mandrel lines as sacrificial features that establish a feature pitch. Sidewall spacers are formed adjacent to the sidewalls of the mandrel lines. After selective removal of the mandrel lines, the spacers are used as an etch mask to etch an underlying hardmask over areas exposed by mandrel removal and areas between the spacers. The pattern is transferred from the hardmask to an interlayer dielectric layer to define trenches in which the wires of the BEOL interconnect structure are formed.
Cuts may be formed in mandrel lines in order to section the mandrel lines and define discontinuities between the sections that subsequently are used to form adjacent wires that are spaced apart at their tips with a tip-to-tip spacing. Non-mandrel cuts may also be formed in the hardmask itself along non-mandrel lines exposed between the sidewall spacers and filled by spacer material when the sidewall spacers are formed on the mandrel lines. A pattern reflecting the cut mandrel lines, the non-mandrel lines, and non-mandrel cuts is transferred to the hardmask and subsequently from the hardmask to form the trenches in the interlayer dielectric layer.
At larger pitch nodes, imperfections in the interconnect lines resulting from self-aligned patterning processes were relatively insignificant. However, as feature sizes have progressively shrunk to sub-10 nanometer pitches, various effects of these imperfections have become magnified, such as increased electrical resistance in interconnect lines and generating shorts between interconnect lines.
Improved methods of self-aligned multiple patterning and structures formed by self-aligned multiple patterning are thus needed.